(i) Technical Field
The present invention relates to a communication apparatus, a communication system, and a computer readable medium.
(ii) Related Art
Internet protocol (IP) facsimile apparatuses that perform digital communication of image information using an IP are available. Some of the IP facsimile apparatuses are capable of performing not only digital communication of image information using an IP but also analog communication of image information via a public switched telephone network (PSTN). Such an IP facsimile apparatus is provided with not only a communication interface compatible with an IP, such as a local area network (LAN) card, but also a communication interface compatible with a PSTN, such as an analog facsimile communication card.
In recent years, communication between facsimile apparatuses using a next-generation network (NGN) has become prevalent. An NGN is an infrastructure network for providing a new information communication service, in which fixed terminal communication and mobile communication are combined, and also telephone communication, data communication, and streaming broadcasting are combined. As an apparatus for relaying communication between the NGN and an IP facsimile apparatus, a relay apparatus such as a home gateway apparatus may be used.
In a case where a relay apparatus such as a home gateway apparatus relays communication between an NGN and an IP facsimile apparatus, an optical fiber connected to the NGN is connected to a corresponding port of the relay apparatus in a typical case. Also, a LAN cable connected to a LAN card provided in the IP facsimile apparatus and a modular cable connected to an analog facsimile communication card provided in the IP facsimile apparatus are connected to corresponding ports of the relay apparatus, respectively.
Typically, when an analog facsimile apparatus connected to a PSTN and an IP facsimile apparatus connected to an NGN perform communication with each other under the situation in which the NGN is connected to the PSTN, analog-to-digital conversion or digital-to-analog conversion is performed by an apparatus that connects the NGN and the PSTN (hereinafter referred to as a network connection apparatus) or a relay apparatus. For example, in the case of transmitting a signal to the IP facsimile apparatus connected to the NGN, the network connection apparatus deems the signal output from the analog facsimile apparatus to be a voice signal, and performs digitalization and packetization on the signal. Such a communication scheme is referred to as a deemed voice communication scheme.
In communication using the deemed voice communication scheme between an analog facsimile apparatus connected to a PSTN and an IP facsimile apparatus connected to an NGN, a session initiation protocol (SIP) may be used for starting, changing, or ending the connection between the communication apparatuses. For example, when a request for starting communication using an IP (for example, an INVITE request in the SIP) is transmitted from an analog facsimile apparatus to an IP facsimile apparatus via a PSTN and an NGN, a relay apparatus receives the request at all the ports thereof. Then, when responses from all the ports are obtained, the relay apparatus performs an arbitration process on these responses to determine an SIP response (for example, on the basis of a predetermined priority), and transmits the SIP response to a network connection apparatus. Also, there is a network connection apparatus that converts a received SIP response into a corresponding audio signal and transmits it to an analog facsimile apparatus.
When a request for starting communication using the deemed voice communication scheme is transmitted to an IP facsimile apparatus on a receiver side under the situation in which the number of analog facsimile apparatuses with which the IP facsimile apparatus is performing analog communication has reached a predetermined number, a response indicating refusal of connection (for example, a 488 response in the SIP) may be transmitted from a relay apparatus to a network connection apparatus as a result of an arbitration process of arbitrating between the response indicating refusal of connection from a LAN port of the relay apparatus (for example, a 488 response in the SIP) and a response indicating that communication is being performed from an analog port of the relay apparatus (for example, a 486 response in the SIP). In this case, there is a possibility that the network connection apparatus converts the response indicating refusal of connection (for example, a 488 response in the SIP) into an audio signal that is different from an audio signal indicating that communication is being performed.